This invention relates to a chemical etchant. In particular, this invention relates to a wet chemical etchant for chromium films that have been patterned with positive photoresist.
Alkaline chromium etchants have been used to etch chromium patterned with negative photoresist. The formulations for these etchants have relatively high concentrations of potassium hydroxide or sodium hydroxide. When used to etch chromium patterned with positive photoresist, this strong alkaline etchant will attack and dissolve the positive photoresist before the chromium film is completely etched away.
In formulating an alternative chromium etchant for use with positive photoresist, it was found that while acidic formulations did not attack positive photoresist, no acidic formulation would reliably depassivate oxidized chromium and etch the chromium metal while still maintaining a high selectivity to other metal layers, such as copper thin film.